A wide variety of sensors are known in the art and are used to detect human or human-like contact with or proximity to the sensors. These sensors typically provide a voltage level that is passed to other circuitry either directly or through a conditioning circuit. This voltage level functions as a trigger or a threshold and is used to determine whether a human or human-like object has requested an operation, or whether a human or human-like object is present. Sensors of this type are often found in electronic devices such as kitchen appliances and are designed to operate through a dielectric substrate in order to provide an easy-to-clean surface such as a glass-ceramic cook top or a flat control panel.
One problem with conventional sensors and control circuits is that they are prone to noise disruption. Contamination is one simple source of noise that can impact a sensor and control system. For example, the glass-ceramic that functions as the dielectric substrate in a cook-top appliance can become contaminated when a substance such as ketchup is spilled over a sensor area. Or a false trigger might be generated by the simultaneous touch of multiple sensors when a damp cloth is used to clean an appliance. In U.S. Pat. Nos. 5,594,22 and 6,310,611 the problem of noise caused by contamination is discussed, and a system is disclosed in which touch sensors are attached to one side of a substrate for detecting user contact on the opposite side of the substrate, thereby separating the touch sensors from the contaminant.
Some sources of noise, however, are not so easily remedied. Conventional sensors and their controls are prone to radio interference from nearby devices such as radio towers, cell phones and other portable radio devices. This type of noise typically appears as spikes on a sensor or on multiple sensors, but can appear as a slower attenuation. In addition, sensors and their controls are prone to electromagnetic noise in the circuitry of the device through such things as cross talk between sensor channels and attenuation of the signals due to noise generated from power supplies or conditioning circuitry. This type of noise can also appear as spikes or slower attenuation and typically affects all sensors in a similar manner.
In an effort to differentiate between a false signal caused by noise and a legitimate request for operation, most sensor controls use well-known techniques for signal filtering in the circuit, as well as standard signal processing. A program in a microcontroller, a specially designed integrated circuit chip or a signal processing circuit typically performs the signal processing function. The signal processing techniques that are known in the art include average readings of the sensor, requiring multiple attenuations to the sensor value across successive readings (possibly in a specified time period), imposing a delay to allow for checking for multiple sensors indicating an event, and masking most or all simultaneous events. Another known technique for handling noise is via signal coupling through a connection to earth ground or the appliance with confirmation of the coupled signal. But while these sensor-signal processing techniques help to reduce the disruptions caused by noise, they often create new problems. For example, these standard techniques reduce responsiveness of the control to input and prohibit operation in the presence of noise. In addition, these techniques strictly limit the use of special functions that require simultaneous key presses for more complex operation of the device.
A unsatisfied need therefore exists in the industry for an improved touch and proximity sensor control system and method that addresses the shortcomings of the conventional systems, some of which have been described above.